The overall aim of this proposal is to further characterize the structure and properties of this novel osteoclast-specific proton pump (OC- H plus/minus ATPase), focusing mostly on the catalytic portion of the transporter and its 63kd subunit and on the unique vanadate sensitive component of this pump. Based upon our preliminary data, this proposal will address the following specific aims: (1) Clone and sequence, using classical and PCR methods, the two catalytic subunits of the OC- H+ATPase in order to determine the molecular basis for the unique nitrate and vanadate sensitivity of this proton pump; the selection of the catalytic subunits as our first targets is based upon the fact that vanadate is known to interact with the catalytic portion of ATPases; (2) Purify the OC- H+ATPase from chicken osteoclasts, in order to characterize the enzyme biochemically and identify the vanadate and nitrate sensitive components(s), and (3) Study the regulation of the expression and function of the OC- H+ATPase by calciotropic and sexual hormones. This program could lead to the development of new therapeutic approaches based upon the unique properties of the OC- H+ATPase and may in the long run allow the specific inhibition of acid secretion by the osteoclast, inhibiting bone resorption in diseases where it is increased (osteoporosis and others).